1) Field of the Invention
The present invention generally relates to active oxygen scavengers for packaging.
2) Description of Related Art
It is well known that limiting exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and “shelf-life” of the product. By limiting the oxygen exposure of oxygen-sensitive products in a container or package, the quality of the products is maintained and spoilage or damage due to oxidation is avoided. In addition, such packaging also keeps the product fresh in inventory longer, thereby reducing costs incurred in disposing of expired products and restocking with fresh products.
Some containers function as a passive barrier to oxygen, i.e. physically isolating the food in the container from the oxygen in the air outside the container. The effectiveness of relying on the container as a passive barrier is limited. Most containers are not air tight; oxygen can diffuse through the container walls over time. Additionally, for oxygen-sensitive solid foods like nuts, the voids and empty space within the container between the nuts and between the nuts and the container wall may contain a significant amount of oxygen that was trapped during packaging.
In order to increase the oxygen barrier effectiveness of the containers, an increasing number of containers are using active barriers to protect oxygen-sensitive products. Active barriers, also referred to as active packaging, entail the use of oxygen scavengers, which are materials that can chemically bind with oxygen in order to capture the oxygen before it can cause damage to the oxygen-sensitive products.
Some packages employing oxygen scavengers rely on an iron-based catalyst. For example, some packages include one or more sachets, which contain an iron-based composition, placed in the interior of the package. The iron-based composition scavenges the oxygen through an oxidation process. However, formation of the sachets requires an additional packaging operation. Also, many consumers are uncomfortable at finding something that appears foreign near their food. Another risk or danger is accidental consumption of a sachet when placing one in a food container. Alternatively, the iron-based compositions are sometimes embedded into the walls of the containers, but this degrades the wall's transparency and mechanical properties. Another drawback to iron-based catalyst is the need for specific atmospheric conditions, specifically high enough humidity, in the package in order for the scavenging to occur at an effective rate.
Other packages contain oxygen scavengers within the wall structures of the package. Typically, the walls are made from a composition of resin, an oxygen scavenger, and a catalyst. Possible scavengers are unsaturated hydrocarbon or ascorbic acid. Often the catalyst is a transition metal catalyst in the form of a metallic salt. Oxidation or the scavenging of oxygen usually begins with such structures as soon as the container or package is formed. However, manufacturers of the containers often must store the containers for a time before the packager will actually use the containers for packaging products. Therefore many of these containers lose their effectiveness before being used. Some oxidizable polymers have been developed which allow for controlled activation with the use of a UV station. However, these types of containers may be prone to premature activation if not shielded properly before packaging.
It would be advantageous, therefore, to have a container or package with an active oxygen scavenger which does not require specific environmental conditions, such as relatively high humidity, and is activated near or at the point where the products are placed within the container or package. Also, it would be advantageous for the presence of the active oxygen scavenger to be essentially undetectable by consumers.